1. Field of the Invention
The present invention relates to an adaptive filter, in particular a method of preventing divergent behavior of the adaptive filter.
2. Description of the Related Art
Adaptive filters have been widely used in the field of communication, for example in adaptive equalizers in transmission lines and adaptive echo cancellers as well as in the field of signal processing, for example in adaptive noise cancellers, adaptive notch filters and adaptive predictors in voice coding.
A problem encounted in an ordinary adaptive digital filter whose tap gains are adjusted through a recursive correction algorithm has been that convergence of a tap gain is not guaranteed under unstable conditions and a tap gain which has once converged to a certain value tends to diverge again due to noise or other interference.
In order to solve this problem, it has been proposed that "a leak" is imposed on the tap gain in every step of the recursive correction so as to suppress such divergent behavior.
However, in this divergence-suppressing adaptive filter, there is a problem that, since tap gain has to be multiplied by a leak coefficient corresponding to the leak at every recursive correction for each tap, the amount of operation necessary for correcting all tap gains markedly increases due to the multiplication. Further, there is another problem that, since tap output is weighted by tap gain which is multiplied by the leak coefficient, the tap gain of the adaptive filter at the time of converging is likely to reach a value which depends on the leak coefficient and which is not optimum in the sense of the least mean square.